Procedures used for dynamically laterally loaded pile tests in a centrifuge

Most of the experimental work carried on pile behavior on centrifuge has been limited to monotonic or cyclic loading, or both. As dynamic loads generated by shocks and earthquakes are difficult to model in centrifuge, not much work has been reported in the literature on the impact mechanism to produce shock in-flight, though seismic loads can be well simulated by in-flight shakers. A complete experimental procedure, i.e., hammering system, measurements, and test procedures, has been developed to test on centrifuge lateral impact on piles. In the first part of the paper following the test procedure, the experimental set-up is detailed from the soil preparation and piles equipment to the horizontal hammering or impact system. Innovative parts of the system such as the impact system and its monitoring are described. The second part describes the feasibility and the practice of the impact device and the adopted procedure to test on centrifuge different types of piles _jacked, cast-in, and 1 g driven_ in sand. The first series of tests are focused on the evaluation of possible errors and influences due to pile position, boundary effects, and repeatability of tests. Scale effects have been studied by carrying out a series of modeling of models tests at 40 and 60 g. In conclusion, all these preliminary centrifuge tests have demonstrated that the complete experimental set-up including the impact system and its use procedure is achieved and able to perform horizontal impacted piles tests on centrifuge

Avaliação estatística da variação da velocidade de propagação de ondas de ultra-som na madeira em presença de defeitos Statistical evaluation of the ultrasonic wave velocity variation in defective wood

Os métodos visuais para a detecção de defeitos na madeira, ainda que de grande utilidade, podem ser falhos e exigem a utilização de mão-de-obra relativamente bem treinada. Muitas vezes, a presença de nós, rachaduras ou, ainda, regiões com medula no interior de uma peça serrada, podem ser imperceptíveis na avaliação visual. Um dos grandes avanços obtidos nos últimos anos na caracterização de materiais, tanto do ponto de vista mecânico quanto da qualidade, é a aplicação de técnicas que utilizam a propagação de ondas, destacando-se, dentre elas, o ultra-som. O objetivo deste trabalho é avaliar, estatisticamente, a possibilidade de se utilizar o método do ultra-som na detecção de defeitos em peças de madeira serrada. Para isto, foram utilizadas 180 peças de dimensões nominais: 0,027 m de espessura; 0,10 m de largura e 0,25 m de comprimento, retiradas de vigas de Pinus sp obtidas em serraria da cidade de Campinas. As peças foram ensaiadas na umidade de equilíbrio ao ar. Para a realização dos ensaios utilizou-se o equipamento de emissão de ondas de ultra-som marca Steinkamp BP-7 com transdutores de 45 kHz. Inicialmente foi realizada uma análise visual das peças e, posteriormente, a determinação da velocidade de propagação das ondas nas mesmas peças. Com os resultados, realizou-se uma análise exploratória das variáveis e obteve-se um modelo de regressão logística visando verificar a relação entre a presença ou não de defeitos e a velocidade de propagação da onda do ultra-som na madeira. Os resultados demonstram uma forte relação entre a velocidade de propagação da onda de ultra-som e os defeitos detectados pela análise visual<br>Visual methods to detect wood defects, although of great utility, can lead to inaccurate results and demand a specialist to carry it out. The presence of knots, cracks or pith regions inside a sawed piece can be imperceptible in the visual evaluation. One of the greatest progress obtained in the last years in the characterization of materials - not only to determine its mechanical properties but also its quality - is the application of acoustic techniques like the ultrasound. The objective of this study is to evaluate, by statistical analysis, the sensibility of the ultrasonic method for detection of defects in pieces of sawed wood. For the trail, 180 pieces of Pinus sp. with 0.027 m of thickness, 0.10 m of width and 0.25 of length were used. These pieces tested under air dried condition (approximately 12% moisture content), were obtained at a saw mill in Campinas. The velocity of ultrasonic waves was measured by Steinkamp BP-7 ultrasound equipment with 45 kHz transducers. Initially the pieces were analyzed by visual method and later the velocity of ultrasonic waves through the wood pieces was measured. An exploratory analysis of the variables was done and a logistic regression model was obtained. The objective was to verify the relationship for the presence or absence of defects in the wood and the velocity of ultrasonic wave propagation. The results demonstrate a strong relationship between the ultrasonic wave propagation and the defects detected by the visual analysi

Etude de definition et de faisabilite d'un instrument de mesure in situ de la permeabilite a l'air des elements du batiment

SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RP 400 (1565) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc